Current transfer measurement along a linearly extended contact

ABSTRACT

Current transfer along a linearly extended electrical contact is determined during or prior to commencing electroplating or other processing of strip material permitting corrective measures directed toward higher yield and higher quality production. Current distribution is determined by measuring the magnetic flux pattern in the strip material along the linearly extended electrical contact. Automated contact control across the strip is obtained responsive to such measurements.

Feb. 29, 1972 w. A. WILSON 3,645,876

CURRENT TRANSFER MEASUREMENT ALONG A LINEARLY EXTENDED CONTACT Filed July 8, 1969 HG PLATING SOLUTION A PRESENT DISPLAY 52 INVENTOR WALTER A. WILSON CONTROL VOLTAGE A CURRENT 1 44 48 BY SM. d6 Q United States Patent 3,645,876 CURRENT TRANSFER MEASUREMENT ALONG A LINEARLY EXTENDED CONTACT Walter A. Wilson, Pittsburgh, Pa., assignor to National Steel Corporation Filed July 8, 1969, Ser. No. 839,853 Iut.,Cl. C23b /00, 5/68 US. Cl. 204-211 3 Claims ABSTRACT OF THE DISCLOSURE This invention is concerned with determining current transfer along a linearly extended electrical contact. In. its more specific aspects the invention is concerned with measuring current distribution across the width of metallic longitudinally continuous material during electrolytic processing such as an electroplating operation.

In electroplating of steel strip, for example in chromium plating, proper distribution of current in the steel strip is important to the production of prime product. The chromium plating process requires high current densities for maximum plating eificiencies and commercially practical plating rates. The high current densities impose stringent operating requirements on the electrical contact rolls used since current transfer is of sufiicient magnitude to cause arcing and damage to the strip due to unbalanced current transfer along the linearly extended electrical contact provided by such rolls.

In addition to possible strip damage, an imbalance in the current density can cause uneven coating. Such imbalances result generally from uneven roll contact pressures which can stem from a number of causes such as variations in strip configuration during processing, and the like. The prior art has been limited to determining the effect of imbalances in current transfer by observation and testing of the product after treatment as no method or means has been provided to the art for determining imbalanced current transfer during processing of continuous strip material.

An important objective of the present invention is to provide for monitoring current distribution or changes in current distribution along a linearly extended electrical contact with strip material. By sensing changes, excessive current transfer at any point along a linearly extended contact means can be anticipated and, the damage to the strip can be avoided by selective corrective measures. Such corrective measures can be carried out automatically responsive to current measurements.

Referring to the accompanying drawings for an illustration of a specific embodiment of the invention:

FIG. 1 is a schematic cross-sectional view of a plating cell of a continuous strip electroplating line,

FIG. 2 is a schematic view of apparatus embodying the present invention, and

FIG. 3 is a schematic view of a portion of the apparatus used in the present invention.

In continuous strip electroplating of steel strip with tin, chromium, and the like, the steel strip is fed successively through a plurality of plating cells. FIG. 1 shows a typical tinplating cell. Continuous strip is fed longi- 3,645,876 Patented F eb. 29, 1972 tudinally between contact roll 10 and backing roll 12 into plating cell 14. The strip is immersed in electrolyte solution 16 and travels in close proximity to anode plating bars 18, 20. Plating current is provided from source 22. Strip 8 is the cathode in each cell and electrical contact is completed through metal contact roll 10. The plating circuit of cell 14 includes plating current source 22, connector 26, cathode contact roll 10, strip 8 (the cathode), electrolytic solution 16, plating bars 18, 20 (the anode), anode support 24 and connector 25.

For uniform coating purposes it is important that the current transfer between the contact roll and the strip be uniform across the full width of the strip to be plated. The present invention measures current distribution across the width of the strip by monitoring the magnetic flux pattern across the width of the strip contiguous to the elongated electrical contact and correlating the incremental magnitude of the flux density across the width of the strip to current transfer along the elongated electrical contact. The magnitude of fiux density is directly proportional to the magnitude of current so that measurement of flux density as provided by the present invention provides an accurate indication of current transfer along the length of the electrical contact.

Referring to FIG. 2, strip 27 is directed downwardly after passage between contact roll 30 and backup roll 31 for submersion in an electrolytic bath (not shown) such as a chromium plating bath. A magnetic flux sensing means 32 is positioned in close proximity to contact roll 30 and strip 27 where they meet for current transfer purposes.

The flux density sensed by the magnetic probe 32 is transferred by signal lead 34 to measuring unit 36 which indicates the flux density at the instantaneous position of probe 32. Unit 36 can readily be calibrated to indicate current density as well as flux density because of their proportionality.

An important concept is the provision for monitoring current distribution or changes in current distribution along the linearly extended contact. In carrying out the invention, probe 32 can be moved at a preselected rate in feet per minute, or other suitable units, across the width of the strip. In an alternative method, a plurality of probes can be positioned at predetermined locations distributed across the width of the strip. Transverse guideway 30 is utilized to permit probe 32 to be moved transversely across the width of the strip or for support of a plurality of probes to be positioned at predetermined locations across the width of the strip. Two additional probes are shown in dotted lines; the number of fixed probes would be dependent on the width of the material, type of probe, and detail of pattern desired.

A probe should be placed as close as possible to the line of contact between roll and strip in order to determine current transfer. Nominally the probe is positioned between about a quarter inch to a half inch from the line of contact. By thus measuring current distribution where current is transferred, current transfer along the linearly extended contact can be accurately determined.

The magnetic probe should be sensitive to magnetic flux magnitude and changes in magnetic flux. In practice a Hall-effect magnetic proble has been found suitable for the present invention. As shown schematically in FIG. 3, a Hall-effect semi-conductor sensing element 40 (typically indium arsenide) is positioned to intercept lines of flux due to current in the strip. In operation, the carriers in the semi-conductor material are deflected by the magnetic field 41 and the control current I provided through leads 42, 44. The Hall voltage (E across leads 46, 48 results from the electric field produced by the deflected carriers. No time rate of change requirement is imposed on the magnetic field. Therefore motion of the strip is unnecessary for a measurement of residual or impressed magnetic field. This permits determination of current transfer under a variety of conditions, independently of strip speed.

In the preferred embodiment the semi-conductor sensing element 40 is positioned so that the magnetic flux parallel to the strip material intercepts element 40 at substantially right angles. With this arrangement accurate and direct correlation of flux density and current transfer is provided and minor variations in current transfer are more readily indicated.

FIG. 2 shows a system in which the pattern of flux densities or current distribution across the width of the strip contiguous to the current transfer contact is indicated on storage oscilloscope 50'. Signal lead 51 interconnects measuring unit 36 and oscilloscope 50. The flux densit pattern, or its proportional current pattern, across the strip can be indicated.

In the specific embodiment shown present display 52 illustrates current distribution at time of measurement. This display can be compared to the pattern from a previously measured display 54. Other types of display with selectable time delays can be utilized for indicating a change in current distribution and projecting changes in current transfer before damage to the product results. Also, a series of individual indicators can be utilized to indicate current levels at preselected locations across the width of the strip and comparison with stored measurements can readily be accomplished with known instrumentation.

The output from measuring unit-36 can be utilized to automatically control pressure distribution along roll 30. For example, if the current being transferred increases at or near one longitudinal roll end of 30, a signal can be generated to automatically decrease the pressure contact between the contact roll 30 and backup roll 31 at that longitudinal end of the rolls. The degree of automated control available is not limited by measurement features of the present invention but is limited only by the presently available teachings on the mechanics of roll positioning under dynamic conditions.

In the embodiment shown the instantaneous position of probe 32 determined by probe position indicator 56 is fed over signal line 58 to a logic and control circuit unit 60. The instantaneous value of flux density or current density from unit 36 is fed over signal lead 62 to control unit 60. Values in excess of a predetermined limit or incremental changes in current transfer adjust pressure along the contact roll 30 by varying the pressure on its longitudinal ends. As shown positioner means 64 for the left end of the contact roll is controlled by left side positioner drive 66 and right side positioner means 68 is controlled by right side roll positioner drive 70. Mechanical means for effecting a change in roll pressure at longi-' tudinal ends of a roll are known in the art and no further description is necessary for an understanding of the invention.

The apparatus shown provides various methods for detecting changes in current transfer and anticipating resulting problems. For example incremental changes at a selected position can be detected, recorded if desired, and used to change roll pressures. The storage oscilloscope provides means for comparison of current transfer across the full width of the strip over selectable comparison periods and/or against selectable standards. Other methods utilizing instantaneous changes in current transfer or incremental changes over selected periods of time will be available to those skilled in the art based on the present disclosure.

Individual measuring units and instrumentation combined in the specific embodiment are commercially available; e.g. the magnetic flux sensing probe 32 and its associated Hall-effect measuring unit 36 are manufactured by Bell Incorporated, Columbus, Ohio, and are designated Model A by that company. The storage oscilloscope is manufactured by Hewlett Packard Corporation of Palo Alto, Calif., and designated Model 141A by that company. During practice of the invention it has been found that these units provide accurate measurements of the total current transferred to within less than 2% of the total current being fed to the contact roll as measured by standard ammeters used in the art.

In a continuous-strip processing line, measuring apparatus can be utilized at each contact roll in the line. While a trip plating operation has been specifically described, the invention is applicable to any strip processing line whether plating, cleaning, heating, or otherwise treating where there is a transfer of current along a linearly extended contact with strip material. The strip material can be a solid continuous material, such as steel strip, or a porous material in strip form, such as wire screening, and

the like, or any longitudinally extended material under circumstances Where it is desired to measure current transfer over a linearly extended electrical contact.

Other flux sensing means, measuring units, indicating instrumentation, contact and control apparatus than those described in the specific embodiment disclosed above can be used without departing from the invention, so that the scope of the invention is not to be limited by such disclosure but rather is to be determined from the appended claims.

What is claimed is:

1. Apparatus for use in continuous strip electroplating for measuring current distribution transversely of the longitudinal direction of the continuous strip, the continuous strip electroplating line including a plating cell having an elongated contact roll at the strip entry side of the plating cell, the elongated contact roll being in electrical contact with the continuous strip across a substantial portion of its width, comprising magnetic flux sensing means for sensing magnetic flux adjacent to the contact between the continuous strip and the elongated contact roll,

support means for the magnetic flux sensing means for preselectively positioning the magnetic flux sensing means across the width of the strip, and

means for measuring current magnitude at preselected locations across the width of the strip responsively to sensed magnetic flux.

2. The apparatus of claim 1 in which the support means includes means for moving the magnetic flux sensing means across the width of the strip at a preselected rate.

3. The apparatus of claim 1 further including means responsive to the means for measuring current magnitude acrossthe width of the strip for adjusting contact between the strip and the elongated contact roll to effect substantially uniform current transfer across the width of the strip.

References Cited UNITED STATES PATENTS 2,455,997 12/1948 Holman 204-211 2,690,424 9/1954 Hassell 204206 3,365,382 1/1968 Godschalk 204-211 3,264,198 8/1966 Wells 20428 OTHER REFERENCES IBM Tech. Disclosure Bull., vol. 6, No. 8, January 1964 by Harris.

FREDERICK C. EDMUNDSON, Primary Examiner U.S. C1. X.R. 204-28, 206 

